WASHINGTON- FBI Director Robert Mueller sees a rising threat from homegrown terrorists but cautions that foreign groups are far from vanquished and still consume more bureau resources.

"We have certainly hundreds" of people in this country that the bureau is investigating with varied levels of intensity, Mueller told a group of reporters Wednesday. "But if you're looking at terrorism across the board ... we have several thousand cases _ although they may be intelligence cases" to gather information rather criminal cases headed for prosecution.

With attention lately focused on the arrests of four groups of largely homegrown plotters in the past year in Miami, Atlanta, Toledo, Ohio, and Torrance, California, Mueller took pains to point out that al-Qaida and other international terrorists still represent a large threat.

"We've decimated al-Qaida's leadership and taken away their sanctuary, but there are still individuals in the al-Qaida hierarchy who are capable of organizing, financing and supporting attacks in the United States or against United States interests around the world," Mueller said.

"One cannot dismiss the potency of al-Qaida to undertake attacks," he added, but there are now also groups here and in other countries "motivated by radical Islamist ideology to undertake actions on their own."

Mueller added that many of the bureau's domestic cases "may have ties overseas."

The number of overall terrorist investigations has remained fairly static for the past two years after spiking immediately after the Sept. 11, 2001, attacks and after passage of the USA Patriot Act, Mueller said.

And FBI Deputy Director John Pistole said, "Many, if not most, of those cases are dealing with material support for terrorism. These are not bomb-throwers; these are people out there raising money or recruiting."

With the rise of homegrown plots here and aboard, Mueller said the bureau is putting some of the new resources it acquired after 9/11 to work on trying "to identify the various stages of radicalization and ... those who would be vulnerable to radicalization and those who would do the radicalization, so you could address them before they could engage" in attacks.

These include doubling the number of FBI intelligence analysts and tripling its linguists and putting analysts in all 56 bureau field offices. At the same time, the FBI has ramped up its regional joint terrorism task forces from 35 to 101 since 2001, expanding the number of federal, state and local agents assigned to them from 1,000 to nearly 4,000.

The FBI is looking at where radicalization can occur. Mueller said this was not necessarily in mosques but anywhere radical fundamentalism could be taught by individuals or even one charismatic individual, including gyms, schools, universities and prisons.

"I hope the American people understand this problem (of terrorism) is going to be with us for a substantial period of time," Mueller said, "and the FBI does a heck of a good job."

He added that the bureau had expanded its resources and transformed its anti-terrorism focus from after-the-fact arrests to prevention while "we've maintained our operational tempo" against public corruption, organized crime, civil rights, corporate crime and gangs.